The present invention relates to a pre-cast heating panel as well as to a method of fabricating same. More particularly, the invention is directed to improvements in heating panels of the type comprising a cement-based material with an electric heating element embedded therein.
Electrically heated ground coverings made of concrete having electric heating wires embedded therein have long been known. These heated ground coverings are particularly useful for driveways, sidewalks, roads or other traffic bearing surfaces for the purpose of maintaining such surfaces free of ice and snow accumulation. They are generally formed at the job site by positioning an electric heating wire in a given pattern, usually a sinusoidal configuration, onto a support material such as sand, gravel or a layer of concrete, and then pouring concrete thereover. The electric wire so installed at the job site is subject to mechanical breakage such as by being threaded over, as well as to electrical short-circuit, for instance, when the moving mass of poured concrete brings two adjacent wires into contact with each other, and it is often after the concrete has been poured over the wire that such failures in the wire are noticed. It thus becomes necessary to locate the exact position where there is a failure in the wire, which may be quite time consuming, and then to proceed to the necessary repairs after having broken the concrete in order to gain access to the embedded wire. This of course adds to the cost of installation.
A number of solutions to these problems have been proposed. In U.S. Pat. No. 3,069,522, for example, a heater element for embeddment in a concrete slab is described, which comprises a plurality of plastic tubes connected adjacent their opposite ends with spacer strips in a manner such that the tubes are held in equidistantly spaced parallel relation with the free ends of the tubes extending beyond the spacer strips. An electrical heater wire is threaded into one outermost tube and then threaded back and forth through the several tubes in a reverse manner to extend outwardly from the opposite outermost tube, thereby forming a plurality of equidistantly spaced flights that are supported and anchored against movement with respect to each other. Such a heater element which is thus prefabricated into a relatively rigid grill may be embodied within the concrete at the point of use or it may be laid directly upon the exposed surface of a prebuilt concrete walk or the like and then covered and bonded to the concrete surface by the application of epoxy resin.
In U.S. Pat. No. 3,573,427, on the other hand, the accumulation of ice and snow on an asphaltic concrete pavement is prevented by the use of an asphaltic concrete made electrically conductive by the addition of graphite particles thereto and by the passage of an electrical current through such asphaltic concrete to generate sufficient heat to melt the ice or snow. The heated ground covering proposed in U.S. Pat. No. 3,626,149 also utilizes a graphited concrete but for improving the thermal conductivity of the concrete, since the use of conventional heating means such as an electrical resistance element embedded in the concrete is retained.
Prefabricated ice and snow melting panels have also been described, for example, in U.S. Pat. No. 2,912,555. In this patent, a relatively stiff insulating board is used to immobilize an electric heating wire which is laced into the board through spaced-apart apertures at each end thereof so as to form several flights of wire overlying the upper surface of the board in substantially equidistantly spaced parallel relation. The board and its assembled wire are then embedded into a molded body of plastic material such as concrete to thereby form a heating panel. A plurality of such heating panels can be laid directly on the ground and anchored in interlocked position to constitute heated driveways, walkways or the like.
Hitherto known heating panels made of concrete such as those described above, whether being prefabricated or formed at the job site, are essentially limited in application to ground coverings due to their heavy weight. It would thus be desirable to have a prefabricated cement-based heating panel of reduced weight that could be easily handled and have a wider range of application, e.g., for heating the walls or floors of buildings.